The present invention relates to a master-information magnetic recording apparatus for recording predetermined master information signals, using a master information carrier, on a magnetic recording medium used in a magnetic recording/reproducing apparatus with large capacity and high recording density.
A magnetic recording/reproducing apparatus has been increasing in recording density in order to achieve its small size and large capacity. Especially, in the field of a hard disk drive as a typical magnetic recording/reproducing apparatus, apparatuses with an areal recording density of more than five gigabits per square inch (7.75 Mbits/mm2) are already available on the market. The practical use of apparatuses with an areal recording density of ten gigabits per square inch (15.5 Mbits/mm2) is expected in a few years. Thus, the technique in this field has been progressing rapidly.
One of the technical features that has enabled such high recording density is the increasing track recording density due to the improvements of magnetic recording media, performance of a head-disk interface, and the like and the advent of a new signal processing method such as xe2x80x9cpartial responsexe2x80x9d. However, recently the rate of increase in track density exceeds that of track recording density greatly, which is a primary factor for the increase in areal recording density. Practical use of a magneto-resistive type head, which is superior to a conventional inductive type magnetic head in reproduction-amplitude performance by far, has contributed to the increase in track density, and has enabled the reproduction of signals from a track whose width is a few microns or less with a high S/N ratio. It is expected that a track pitch will reach the sub micron range in the near future along with further improvement of the head performance.
A conventional hard disk drive has areas (hereafter referred to as xe2x80x9cpreformat recording areasxe2x80x9d) where master information signals such as a tracking servo signal, an address data signal, and a reproduction clock signal are recorded, so that a magnetic head can scan such a narrow track correctly and reproduce the signals with a high S/N ratio. The preformat recording areas are spaced at predetermined angles over the circumference of a disk, that is, over 360 degrees. The magnetic head reproduces such signals every redetermined period to verify its position and corrects its displacement in a radial direction of magnetic disk as required, thus scanning a track correctly.
The master information signals such as a tracking servo signal, an address data signal, and a reproduction clock signal are to be reference signals for the magnetic head to scan a track correctly. Therefore, precise track-positioning accuracy is required in recording the signals. In a conventional hard disk drive, a magnetic disk and a magnetic head are incorporated into a drive in advance. Then the master information signals are recorded with the unique magnetic head incorporated in the drive, using a special servo track recording apparatus. In this case, the preformat recording is performed while an external actuator equipped with the servo track recording apparatus precisely controls the position of the unique magnetic head incorporated in the drive, thus securing the required track-positioning accuracy.
However, the above mentioned preformat recording with the unique magnetic head incorporated in the drive using the special servo track recording apparatus in the prior art has some problems as follows.
The first problem is that the preformat recording requires a long time in the above-mentioned method, since the recording using a magnetic head is basically linear recording by utilizing relative movement between the magnetic head and a magnetic recording medium. In addition, the servo track recording apparatus is quite expensive, thus increasing the cost required for the preformat recording.
The first problem would become more serious along with the increase in track density in the magnetic recording/reproducing apparatus. In addition to the increase in the number of tracks in the radial direction, the following reasons cause the increase in the time required for the preformat recording. That is, the more the track density increases, the greater the precision that is required for positioning the magnetic head. Therefore, preformat recording areas where the information signals such as the tracking servo signal and the like are recorded have to be located at a smaller angular interval over one rotation of the disk. Consequently, the preformat information signals to be recorded in the disk increase as the recording density increases. Thus, more time is required for the preformat recording.
Although the magnetic disk media have tended to be decreased in diameter, disks with a large diameter of 3.5 or 5 inches are still in demand. In a disk, the larger the recording area is, the more the preformat information signals to be recorded increase. The time required for the preformat recording greatly influences the cost performance of such large disks.
The second problem is that due to the space between the magnetic head and the magnetic recording medium and diffusion of the recording magnetic field caused by the shape of a pole provided at the tip of the magnetic head, magnetization at the track edges of the recorded preformat signals lacks steepness in transition.
The recording using a magnetic head is basically dynamic linear recording by utilizing relative movement between the magnetic head and a magnetic recording medium. Therefore, a certain space between the magnetic head and the magnetic recording medium cannot be avoided in view of the interface performance between them. Further, as shown in FIG. 2, a conventional magnetic head usually has two components performing recording and reproduction respectively. Consequently, the width of a pole 22 at a trailing edge of a recording gap corresponds to a recording track width, and the width of a pole 23 at a leading edge is several times larger than the recording track width.
Both the two conditions mentioned above may cause the diffusive recording magnetic field at recording track edges. As a result, such problems occur that the magnetization at the track edges of the recorded preformat signals lacks steepness in transition or erased areas appear on both sides of a track edge. In a current tracking servo technique, magnetic-head position is detected based on a change amount of reproduction amplitude when the magnetic head deviates from a track to scan. Therefore, it is required not only that the magnetic head scan a track correctly with a high S/N ratio as in reproducing data signals, but also that the amount of reproduction amplitude is steeply changed when the magnetic head deviates from a track to scan, i.e. the off-track characteristic is steep. Consequently, when a magnetization at an edge of a track of the preformat signals lacks steepness in transition, it is difficult to realize the precise tracking servo technique that is required for a submicron track recording in the future.
In order to solve the aforementioned two problems in the preformat recording using a magnetic head, Japanese Laid-open Patent Publication (Tokkai Hei) No. 10-40544 proposes a new preformat recording technique. In this technique, a master information carrier is prepared, which comprises a substrate on which a ferromagnetic film pattern corresponding to preformat information signals is formed. The surface of the master information carrier is brought into contact with a surface of a magnetic recording medium. Then, the ferromagnetic film pattern formed on the master information carrier is magnetized, thus recording a magnetized pattern corresponding to the ferromagnetic film pattern into the magnetic recording medium. According to this preformat recording technique, an excellent preformat recording can be performed efficiently with no sacrifice in other important performance such as S/N ratio of the recording medium and interface performance.
FIG. 2 shows a configuration of a magnetic head incorporated in a common hard disk drive and is a plan view seen from the face of the magnetic head that opposes a magnetic disk. The magnetic head comprises a recording head formed of a pole 22 at a trailing edge and a pole 23 at a leading edge, a reproducing element 21, and a lower shield 24. In this case, in an in-plane in which the magnetic head opposes the magnetic disk, xe2x80x9ca head-gap length directionxe2x80x9d is defined as the direction in which the lower shield 24, the reproducing apparatus 21, and the poles 23 and 22 are arranged sequentially. Similarly xe2x80x9ca head-gap width directionxe2x80x9d is defined as the direction perpendicular thereto. FIG. 1 is a plan view showing a schematic configuration of a common hard disk drive.
As shown in FIG. 1, when a magnetic head 11 mounted on a head suspension 13 scans tracks on a magnetic disk, the magnetic head 11 is moved on an orbit shown by the alternating long and short dash line 17 in FIG. 1 by a voice coil motor 15. The orbit generally has a circular-arc shape taken with a rotation axis 18 of a head actuator as its center. The tangential direction at arbitrary points on the circular arc substantially coincides with the head-gap width direction. This tangential direction is defined as the xe2x80x9ctrack-scanning directionxe2x80x9d. FIG. 3 is an enlarged view of a part of a recording track on a magnetic disk 12. Generally, the magnetized direction of bits 31 recorded in the magnetic disk 12 coincides with the head-gap length direction and is perpendicular at every portion to the head-gap width length, i.e. the track-scanning direction of the magnetic head 11.
Therefore, in order to allow the preformat recording technique using a master information carrier to be really effective, it is preferable that the magnetized direction of a ferromagnetic film pattern formed on the master information carrier and the head-gap length direction coincide with each other in preformat recording. That is to say, it is preferable that the magnetized direction of the ferromagnetic film is perpendicular at every portion to the track-scanning direction of the magnetic head in every track on the magnetic disk. When the preformat information signals recorded in the magnetic disk are reproduced using a magnetic head, the magnetic head detects the change in magnetization in the head-gap length direction. Therefore, when the magnetized direction of the ferromagnetic film does not coincide with the head-gap length direction, the reproduction amplitude decreases, which might hinder excellent track-scanning by the magnetic head. The term xe2x80x9ctrack-scanningxe2x80x9d used herein means the scanning performed across tracks.
Thus, it is important that a device for applying a magnetic field used for recording preformat information signals can adjust the applied magnetic field to correspond to a circular-arc orbit of the magnetic head in track-scanning.
The present invention aims to solve the aforementioned problems in the prior art. It is an object of the present invention to provide a master-information magnetic recording apparatus enabling highly reliable preformat recording. In more detail, the object is to provide the master-information magnetic recording apparatus in which when magnetizing a ferromagnetic film pattern formed on a master information carrier, the magnetizing direction of recording bits of the ferromagnetic film pattern coincides with a head-gap length direction of a magnetic head in a magnetic recording/reproducing apparatus.
In order to attain the aforementioned object, the master-information magnetic recording apparatus according to the present invention has a construction as follows: The apparatus has a construction for recording predetermined information signals into a magnetic recording medium having a ferromagnetic layer, by using a master information carrier comprising a substrate on which a ferromagnetic film pattern corresponding to predetermined information signals is formed. The apparatus comprises a support for holding a magnetic recording medium in contact with the master information carrier; and means for applying a magnetic field to the master information carrier to magnetize the ferromagnetic film pattern. The direction of the applied magnetic field being perpendicular to a circular-arc path on the magnetic recording medium along which a magnetic head scans tracks in a magnetic recording/reproducing apparatus into which the magnetic recording medium is installed.
Such a construction allows the magnetized direction of the recorded bits of the preformat information signals on the magnetic recording medium to coincide with the head-gap length direction of the magnetic head in the magnetic recording/reproducing apparatus, thus enabling the preformat recording that permits sufficient reproduction amplitude for track-scanning by the magnetic head in the magnetic recording/reproducing apparatus to be obtained.
The device for applying a magnetic field can be a bar-like permanent magnet with a center axis curved along the circular-arc orbit and its magnetizing direction perpendicular to the center axis.
Further, the device for applying a magnetic field can be a large magnetic head having a pair of bar-like magnetic bodies opposing each other, between which a center axis curved along the circular-arc orbit is located, and a coil wound around at least one of the bar-like magnetic bodies, and its magnetizing direction is perpendicular to the center axis.
Both the constructions mentioned above allow the magnetized direction of the recorded bits of the preformat information signals on the magnetic recording medium to coincide with the head-gap length direction, thus enabling the preformat recording that permits sufficient reproduction amplitude for track-scanning by the magnetic head in the magnetic recording/reproducing apparatus to be obtained.